1. Field of the Invention
The present invention relates to the field of semiconductor packaging. More specifically, the invention relates to fabrication of wafer level packages for electronic devices.
2. Background Art
Wafer level packaging permits a semiconductor die and package to be manufactured and tested prior to wafer singulation. Many electronic devices, such as microelectromechanical systems (“MEMS”) devices, bulk acoustic wave (“BAW”) filters, surface acoustic wave (“SAW”) filters, and many RF devices, require a wafer level package with a cavity around the device to achieve the best performance. However, conventional wafer packaging techniques are costly and, in some applications, the wafer level package can amount to approximately 40% to 90% of the total device cost.
Prior solutions have required numerous, difficult, and costly process steps to achieve a wafer level package with a cavity. The conventional method typically involves spin coating and photo patterning a sacrificial layer over a semiconductor wafer to cover the active device area. Next, a polymer layer is spin coated over the whole wafer, which is photo-patterned to form the permanent package structure and release holes. Then the sacrificial layer is etched out or removed through the release holes to create cavities around the active devices. If the release holes are too small, completely removing the sacrificial layer without leaving any residue on the active device can be challenging and time consuming, and can result in yield loss. If the release holes are too big, the polymer layer can cave in over the active device. Finally, an additional polymer layer must be formed to seal the release holes to complete the cavity around the active device.
In another conventional method, individual “lids” are designed and placed over each active device on the semiconductor wafer. Since each active device must be individually sealed, this “pick and place” serial process can be very time consuming and costly to implement. Thus it can be seen that there is a need in the art for an efficient and inexpensive wafer level package accommodating cavities without the shortcomings of the conventional wafer level packages.